Patent GB-449302-A (GB)
Title: Improvements in and relating to electric musical instruments
IPC: G10H1/18
Filed: 1935-01-23
Abstract: 449,302. Electrical musical instruments. HOBSON, P. T., 63, Belsize Avenue, Hampstead, and HILL & SON & NORMAN & BEARD, Ltd., W., 372, York Road, Holloway, both in London. Jan. 23, 1935, No. 1926/36. Divided out of 432,960. [Class 88 (ii)] The frequency of a back-coupled oscillating- valve circuit 1, feeding a loud-speaker LS, through an amplifier, if necessary, is controlled by keys or pedals, P1, P2, &c., which energize electromagnetic note-relays R1, R2, &c. The latter switch capacities GC1 &c. and/or inductances and adjustable tuning- resistances tr1 &c., across a grid coil 2 of the valve, and, if desired, capacities AC1 in series with its anode coil 3, thus determining the pitch of the note to be keyed. To balance the apparent aural strength of each note, adjustable resistances r1 &c. are also switched across the loudspeaker input. The pedal-keys P1 are supplied with current through self-made contacts M1 &c. on the " melodic " system, whereby when one pedal is depressed, all the pedals on one side of it are rendered inoperative by the breaking of the particular contact M1. Two different note-strengths are provided by stopkeys SK, which switch resistances 5 across the loud-speaker and may be operated through electromagnetic relays. Stops for note-quality may be arranged to switch different oscillatory valve circuits, or to vary the circuit members of a single-valve circuit. Depression of any pedal P1 energizes a corresponding note-relay R1, through the combined action of three relays 7, 8, 9, in the common circuit of all the note-relays, and acting jointly to prevent clicking in the loud-speaker and the simultaneous operation of more than one note-relay. Clicking is prevented by the provision of a resistance 10 shunted across the loud-speaker and gradually increased by reason of the relay 9 wiping over it. The relay 9, which is energized by an additional pedal-contact 11, is slowacting and switches in the supply to the common relay 7 before switching in the loud-speaker by increasing its shunt resistance 10. Sustaining- contacts S are completed by the note-relays R1 themselves, and these hold the note-relays on until after the relay 9, and hence the loudspeaker are cut off. If a second pedal is depressed as the first is released, the sustaining contact S of its relay holds the latter, and the consequent doubling of the current in the common relays energizes the previously inoperative lower-powered relay 8, thereby breaking the circuit and releasing the first relay. Alternatively, in Fig. 2 (not shown), the valve circuit includes a large condenser, sufficient to prevent the valve oscillating, which is switched out by a relay after a noterelay has operated and is switched in again before the note-relay opens. The large condenser is prevented from being switched out unless one of the stop-keys, above referred to, is operated, a further relay being provided for this purpose. In the form shown in Fig. 3, for sounding two notes simultaneously, there are two series of relays aRl, aR2, &c., bR2, bR3, &c., each series controlling an independent valve-circuit like that in Fig. 1. The pedals P1 are connected to arms A1, and both receive their current on the "melodic" system, in such a manner that depression of a first pedal energizes its relay aR1, and a second pedal its relay bR2, all other relays aR1 to the right of the first pedal, and all others bR2 to the right of the second being cut off. With reference to Fig. 4 (not shown), is described an arrangement for sounding three notes at a time. One valve-circuit is arranged somewhat similar to that shown in Fig. 1, with the exception that the " melodic " system is applied to selectorrelays controlling the note-relays, instead of to the pedal-keys themselves, whilst two other valve-circuits are controlled on a double " melodic " system similar to that in Fig. 3, but, again, with the system applied to selector-relays.